The invention relates to a valve control, and more particularly to an interface for a computer operated ball valve actuator that allows for flow control without volume displacement. The invention is particularly useful in laboratory testing and other processes requiring high precision flow control.
In certain laboratory processes, it is necessary to open and close fluid lines in a piping or plumbing system with no resulting volume displacement. In laboratory soil testing, for example, the piping system is often water saturated and of very low compliance. Accordingly, volume displacement associated with the operation of normal valves can cause pressure surges and fluctuations in the system which may alter specimen behavior, corrupt measured constitutive properties data and invalidate the test. Additionally, under certain conditions, sensitive electronic measurement devices used in the piping system could be damaged or destroyed by the use of volume displacement valves. For these reasons, ball valves are used for soils and other critical laboratory testing where volume control is critical and in hydraulic networks where frictional losses resulting from fluid flow must be minimized. Ball valves are configured with an orifice drilled through a cylinder or sphere in the valve stem such that no volume is displaced as the orifice within the stem is turned perpendicular to the flow, closing the associated line. If it is desired to automate a laboratory soils test or a process involving a hydraulic network where frictional losses must be minimized, then ball valves controlled by a computer or other logic network is required.
A commercially available system to open and close ball valves consists of an air operated, double acting load cylinder, a rack and spur gear and a ball valve. Air pressure, controlled by a four-way solenoid valve, drives the load cylinder which moves the rack and turns the spur gear which is attached to the stem of the ball valve. This known arrangement allows the valve to be opened or closed in response to directed air pressure pulses. Some disadvantages are evident in this system, most notably, the arrangement is physically large in size, it is high cost, and it is mechanically complex. The requirement for an air pressure supply for the solenoid valve is particularly inconvenient. Further, the system produces electronic noise which can upset delicate individual electronic circuits. Further, present commercially available systems have no accompanying electronics to allow communication or interface with other devices or with a logic network.